Final answer:
An epidemiologist plays a crucial role in ongoing surveillance and monitoring of disease outbreaks and trends by collecting data, tracking the spread of diseases, and identifying the mode of transmission. They also develop strategies and design policies to control and prevent diseases.
Step-by-step explanation:
An epidemiologist plays a crucial role in ongoing surveillance and monitoring of disease outbreaks and trends. They collect data about a particular disease, track its spread, and identify the original mode of transmission. This information is used to develop strategies and design public health policies to reduce the incidence of a disease or to prevent its spread. Epidemiologists also conduct rapid investigations in case of an outbreak to recommend immediate measures to control it.